From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Michael Glaesemann <grzm(at)seespotcode(dot)net>, David Fetter <david(at)fetter(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: minimal update |
Date: | 2008-03-07 16:10:41 |
Message-ID: | 200803071610.m27GAfV00596@momjian.us |
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Thread: | |
Lists: | pgsql-hackers |
I assume don't want a TODO for this? (Suppress UPDATE no changed
columns)
---------------------------------------------------------------------------
Andrew Dunstan wrote:
>
>
> Tom Lane wrote:
> > Michael Glaesemann <grzm(at)seespotcode(dot)net> writes:
> >
> >> What would be the disadvantages of always doing this, i.e., just
> >> making this part of the normal update path in the backend?
> >>
> >
> > (1) cycles wasted to no purpose in the vast majority of cases.
> >
> > (2) visibly inconsistent behavior for apps that pay attention
> > to ctid/xmin/etc.
> >
> > (3) visibly inconsistent behavior for apps that have AFTER triggers.
> >
> > There's enough other overhead in issuing an update (network,
> > parsing/planning/etc) that a sanely coded application should try
> > to avoid issuing no-op updates anyway. The proposed trigger is
> > just a band-aid IMHO.
> >
> > I think having it as an optional trigger is a reasonable compromise.
> >
> >
> >
>
> Right. I never proposed making this the default behaviour, for all these
> good reasons.
>
> The point about making the app try to avoid no-op updates is that this
> can impose some quite considerable code complexity on the app,
> especially where the number of updated fields is large. It's fragile and
> error-prone. A simple switch that can turn a trigger on or off will be
> nicer. Syntax support for that might be even nicer, but there appears to
> be some resistance to that, so I can easily settle for the trigger.
>
> cheers
>
> andrew
>
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--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://postgres.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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